1. Field of the Invention
The present invention relates generally to energetic materials, and in particular to a method and a composition to substantially instantaneously changing the shock compression sensitivity explosives, propellants, and the like through the compounded addition of distributed SMART materials and the application of an external electromagnetic field.
2. Description of the Related Art
Geoffrey P. McKnight, in a UCLA paper entitled MAGNETOSTRICTIVE MATERIALS BACKGROUND teaches that magnetostrictive materials are broadly defined as materials that undergo a change in shape due to a change in the magnetization state of the material generally these materials are referred to as “SMART Materials.” Nearly all ferromagnetic materials exhibit a change in shape resulting from magnetization change. In most common materials, nickel, iron, and cobalt, the change in length is on the order of 10 parts per million (see FIGURE at right). In addition, the change in volume is very small. This type of magnetostriction has been termed Joule magnetostriction after James P. Joule's discovery in the 1850's. The relatively small change in shape of these materials limited their use in engineering. Initial sonar designs contemplated exploiting the magnetostrictive effect, but were left unexplored due to advances in piezoelectric materials such as quartz and Rochelle salt, and later lead zirconium titanate (PZT). The engineering era of magnetostrictive materials began with the discovery of giant (1000's of ppm) magnetostriction in rare earth alloys during the 1960's by A. E. Clark and others. The culmination of research into an engineering alloy incorporating rare earth materials was Terfenol-D, a specially formulated alloy of Terbium, Dysprosium, and Iron that exhibits large magnetostriction at room temperature and relatively small applied fields. Earlier alloys exhibited large magnetostriction, but either at very large magnetic fields, or at cryogenic temperatures, or both. Terfenol-D overcame the temperature difficulty by incorporating a RFe2 microstructure which raised the curie temperature above room temperature. The necessary magnetic field was reduced by balancing the ratio of Terbium and Dysprosium, two elements with oppositely signed magnetocrystalline anisotropy, such that effective anisotropy of the compound was near zero at room temperature. Since this time, Terfenol-D has become the preeminent magnetostrictive material, although research continues into new materials constantly.
Judy Lin-Eftekhar in a UCLA paper entitled MATERIALS ON THE MOVE: ENGINEERING SMART MATERIALS reports an innovation at UCLA, was the creation of a NiTi “microbubble” that can function as a two-way actuator. Starting out as a perfectly flat disk, it plumps up into a bubble when electric current is passed through the NiTi, heating the material up. When the current is turned off, the bubble recedes and the disk resumes its original shape.